1. Field of the Invention
The present invention relates to a radiation image detection device and a method for manufacturing the same that are used in radiation imaging.
2. Description of the Related Art
In recent years, in the medical field, a radiation image detection device that emits radiation (for example, X-rays) from a radiation source toward an imaging region of a subject (patient) and converts the radiation transmitted through the subject into electric charges to generate a radiation image is used to perform diagnostic imaging. There are a direct conversion type radiation image detection device, which directly converts a radiation into electric charges, and an indirect conversion type radiation image detection device, which converts radiation into visible light first and converts the visible light into electric charges.
The indirect conversion type radiation image detection device includes a scintillator (phosphor layer) that absorbs radiation and converts the radiation into visible light and a photoelectric conversion panel that detects the visible light and converts the visible light into electric charges. For the scintillator, cesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S: GOS) is used. The photoelectric conversion panel is formed by arraying thin film transistors and photodiodes in a matrix on the surface of the glass insulating substrate.
In the case of CsI, the manufacturing cost is high compared with GOS. However, since CsI has high conversion efficiency of radiation to visible light and has a columnar crystal structure, the SN ratio of image data is improved by the light guide effect. Accordingly, CsI is used especially for a scintillator of a high-end radiation image detection device.
For the radiation image detection device that uses CsI for a scintillator, a bonding method and a direct deposition method are known. In the bonding method, a deposition substrate having a deposited scintillator and a photoelectric conversion panel are bonded to each other with an adhesive layer interposed therebetween so that the scintillator faces the photoelectric conversion panel. In the direct deposition method, a scintillator is deposited directly on the photoelectric conversion panel. In the bonding method, since the distal end of the columnar crystal of CsI is close to the photoelectric conversion panel and visible light emitted from the distal end is efficiently incident on the photoelectric conversion panel, a high-resolution radiation image is obtained. However, the bonding method requires a deposition substrate. Therefore, since the number of manufacturing steps is increased, the cost is increased.
In contrast, the direct deposition method does not require the deposition substrate. For this reason, the number of manufacturing steps is small, and the cost is low. In the direct deposition method, since the distal end of the columnar crystal of CsI is disposed on the opposite side to the photoelectric conversion panel, the quality of a radiation image is slightly inferior to that in the case of the bonding method, but is better than that in a case where the scintillator is formed of GOS. For this reason, the direct deposition method is well balanced in terms of performance and cost.
Since CsI is dissolved by moisture, that is, has a deliquescence, a scintillator formed of CsI is covered with a scintillator protection film having a moisture-proof property. For example, in the radiation image detection device disclosed in JP2006-078471A, a scintillator deposited directly on a photoelectric conversion panel is covered with a scintillator protection film formed of hot melt resin, and a peripheral portion of the scintillator protection film is in close contact with the substrate (photoelectric conversion panel). The peripheral portion of the scintillator protection film is brought into close contact with the substrate by performing hot pressing that is to press the target more strongly than other portions while applying heat.
In addition, in the method for manufacturing a radiation image detection device disclosed in JP2006-078471A, when covering the scintillator with a scintillator protection film, first and second steps are used. In the first step, a sheet-like scintillator protection film formed of hot melt resin is made to face the scintillator deposited directly on the photoelectric conversion panel, and the scintillator protection film is brought into close contact with the scintillator and the photoelectric conversion panel by the diaphragm rubber of a vacuum bonding device. In the second step, the peripheral portion of the scintillator protection film is hot-pressed using a heat pressing device.